The referenced literature Wolfgang Walenski: "Einfuhrung in den Offsetdruck"("Introduction to Offset Printing") describes a printing machine for offset printing in which a sheet is passed between two blanket cylinders, each one of which has a plate cylinder associated therewith, and each plate cylinder has its own inker and damper. Prime-and-verso printing is carried out by this machine at the same time. This type of machine requires a separate printing arrangement for prime printing and for verso printing. Some printing machines only include a system for prime printing, and expansion of such a system to permit double-sided printing is not possible since machines designed for prime printing only do not provide space for an additional plate cylinder. Constructing printing machines to be universally applicable for prime and verso printing is frequently uneconomical if, usually, only prime printing is to be effected, and double-sided printing only occasionally. The substantially higher price of a machine having two separate printing systems, one for each side of the sheet, mitigates against such an arrangement unless it is to be used continuously.
Attempts have been made to design machines which are primarily arranged for one mode of printing, but which are more versatile in that change-over to different modes of printing is also possible. The machine described in U.S. Ser. No. 353,235, now U.S. Pat. No. 4,414,896, Nov. 15, 1983, by the inventor hereof, describes a sheet rotary offset printing machine which, selectively, can be used for prime printing or prime-and-verso printing. The machine is so constructed that change-over from prime printing to double-sided printing causes the output per unit time to be half of that of prime printing only. The number of colors which are available for prime printing is decreased by the number of colors which are used for verso printing. Thus, if the machine is used for two-color prime printing, change-over for double-sided printing enables printing on the prime and verso sides only with one color.
A different type of machine is described in German Patent DE-PS No. 21 39 830, based on an invention by the inventor hereof, which describes a multiple printing machine system in which substrate sheets are supplied from a make-ready table to a first printing station having a plate cylinder, a rubber blanket cylinder and an impression cylinder, as is customary in the field. To permit multi-color printing, a group of such printing stations is arranged serially between the make-ready table and a removal apparatus with itermediate transfer drums providing for transport of sheets between the respective printing stations. One or more of such transfer drums may be provided and, additionally, the sheets transported to the respective printing stations, or removed therefrom, are supplied by, respectively, supply drums or removal drums. Each one of the printing stations has its own respective plate and blanket cylinder, with the associted inkers and dampers, and an impression cylinder. The sheet is transferred or passed from a supply drum, transfer drums, and removed from a removal drum after having been printed between the blanket cylinders and the respective impression cylinders of the respective printing stations. In accordance with the disclosure of this patent, it is additionally possible to apply verso printing by so arranging one or more of the transport drums, that is, the supply drum, the transfer drums and the removal drum, that it can carry a printing plate, and to associate an inker with the printing plate.
Double prime-and-verso printing using the direct lithographic printing mode in which the plate cylinder engaging, for example, the prime side of the printing substrate sheet forms the impression cylinder for the plate cylinder applied to the verso side of the sheet--and vice versa--has been described in British Pat. No. 1,328,257, Dahlgren, to which U.S. patent application Ser. No. 862,789, filed Oct. 1, 1969, corresponds. In order to permit double-sided printing, the printing plate applied to the plate cylinder has a hard, durable surface into which ink-receptive image areas are etched to form recesses. These recesses are etched into a dampening fluid receptive surface. Ink is suplied to the recessed image areas of the printing plate, and dampening fluid is supplied to the remaining surface area of the printing plate, such that the surface rejects ink. The printing image is deep-etched into a metal printing plate, for example a trimetal plate.
German Patent Publication Document DE-OS No. 21 34 397, Brodin et al, describes a printing machine which is primarily designed for two-color prime and single-color verso printing, in which a substrate sheet is passed between two rubber blanket cylinders, each having their own inkers and dampers associated with respective plate cylinders, to effect, simultaneously, prime and verso printing from the plate cylinders associated with the two rubber blanket cylinders. A further prime printing image can be transferred by an additional rubber blanket cylinder in engagement--with the substrate sheet between--with one of the rubber blanket cylinders. The additional rubber blanket cylinder has its own plate cylinder, and damper and inker associated therewith. The disclosure includes the comment that, upon use of another method customary in offset printing, the so-called lithographic printing, three impressions can be applied to one side, and no impressions to the other. In this type of operation, the path of the paper web will have to be changed to wrap around one of the rubber blanket cylinders--for example the one previously applying the verso printing, and utilizing the previously used rubber blanket cylinder as an impression cylinder for the plate, which previously was associated with the rubber blanket cylinder now functioning as the impression cylinder.
Various types of printing machines--see, for example, the above-referenced literature--utilize sheet turning drums between successively located printing stations. In such apparatus, a sheet which is passed between two serially arranged printing stations is turned over, so that the second printing station, rather than printing on the same side--for example the prime side--of a sheet, will then print on the reverse, that is, the verso side. Such sheet turning apparatus, in some machines, can be added subsequently as attachments. They have some disadvantages since set-up of the machine for dual-sided printing is much more time-consuming than set-up for single-sided printing only. Further, in order to prevent increased production of scrap, attachments which control the path of the sheet, and utilizing compressed air or suction zones, must be installed. The sheets tend to smear at the turn-over region. The coverage of printed material on the substrate sheet is decreased since a margin must be left not only on the top side, for example, but a similar margin on the bottom in order to permit gripping at the two ends of the sheets by grippers of the turn-over apparatus. Thus, the overall format and coverage of the sheet is not utilized as efficiently as coverage in single-sided printing.